> The "speculator" was placed into the mix with a limited role for providing liquidity
This makes no sense. Who did the placing? Every market has speculators, and even end-user-buyers base their decisions in some part on speculation.
The speculator has no altruistic diktat to provide liquidity. The speculator is there to make money, and providing liquidity is a side-effect. i.e. the speculator wants to take on a position, but can only do this if someone else wants to exit a position -- thus making a trade. The seller's interests are served just as much as the buyer's.
Now, there is a clear issue with cornering the market. However, there is a natural check to this behavior, in that taking delivery of millions of barrels of oil is expensive. And if you have no intrinsic need to consume a commodity, then it is very expensive to sit on. If supply is indeed artificially constricted by hoarding speculators, they will need to sell off their supply at some point.